1. Field of the invention
The present invention relates, in general, to a photomask useful to the exposure of a photosensitive film of a semiconductor device to a light and, more particularly, to a photomask capable of accomplishing the exposure with a small amount of energy, thereby saving the energy.
2. Description of the Prior Art
Generally, in order to form a predetermined pattern, a series of processes must be carried out, that is, coating a photosensitive film on a wafer, exposing it to a light along with a photomask and developing it. When a contact hole is to be formed, a greater energy of irradiating light is required than when other patterns are to be formed.
In order to better understand the background of the present invention, description for a conventional photomask will be given next with reference to some figures.
First, referring to FIG. 1, there is a plan view showing a photomask according to a conventional technique. In this photomask, a region for the exposure of photosensitive film to a light by which a contact hole will be formed is made of a non-chrome material 3, and the other regions are formed of a chrome layer 2.
Referring to FIG. 2, there is shown a result of the exposure to a light using the conventional photomask of FIG. 1. As shown in these figures, on being irradiated on the conventional photomask in a stepper, a light is blocked in the regions of chrome layer 2 atop a quartz substrate 4, whereas it penetrates through the quartz substrate below the non-chrome region and reaches predetermined portions of a photosensitive film 7 placed on a wafer 9. The irradiated, predetermined portions of the photosensitive film 7 are eliminated in a subsequent developing process.
FIG. 3 shows the intensity of the light irradiated over the photosensitive film, indicating that the non-chrome region has higher intensities than the other regions.
As will be expected, the exposure to a light using the conventional photomask is problematic in that if the chrome layer occupies a greater part of the photomask, like a contact hole mask, a greater energy for the exposure is required. In addition, in case of using a stepper with a low power, a high degree of resolution is difficult to obtain with the conventional photomask.